Medical tubing and catheters are widely employed for many treatment and diagnostic procedures involving the administration of fluid medications to the patient and the removal of fluids from the patient. In the broadest sense, medical tubing and catheters are synonymous, a catheter being merely a tube with an appropriately formed tip. However, the ultimate use for which medical tubing is designed requires that the tubing have certain physical characteristics. For example, a catheter must be sufficiently stiff or rigid to enable its insertion and movement through narrow body orifices and channels. On the other hand, tubing as well as a catheter, must be sufficiently flexible so that it may readily conform to body shapes and also be conveniently connectable to medication reservoirs or fluid evacuation containers. In addition, a catheter must be of sufficient mechanical strength to resist tear in normal use, i.e., removed against tissue resistance.
During actual use with a patient, medical tubing is often subjected to forces or stresses that affect its ability to properly function. For example, the patient may roll over onto the tubing and thereby tend to collapse, pinch or bend it. Where a substantial length of tubing is employed, the same can become snagged, knotted or sharply bent to form a kink which impedes or blocks fluid flow. Similarly, catheters placed inside the body can be subjected to twisting and kinking motions due to movement of muscles, bones, etc., adjacent to or surrounding the catheter. Pinch valves or the like also create potentially destructive compressive forces. Obviously, any blockage or impediment of fluid flow can create serious health problems. It is thus recognized by those skilled in the art that medical tubing desirably should be able to resist collapse and the formation of kinks and also be able to quickly and completely recover from the imposition of such forces.
Medical tubing and catheters are generally made by well known extrusion processes of single polymers The most widely used materials of construction are thermoplastic polyamides (nylons), Teflons and polyurethanes, which possess a wide range of stiffness and mechanical strength properties. Experience has shown that they either suffer from an inability to quickly and completely recover from severe strains applied thereto or exhibit low mechanical strength or poor kink recovery properties
Flexible materials known to possess good elastic recovery are too soft for proper insertion. Rigid materials needed for their abuse resistance exhibit poor recovery from kinks No single material is known to meet all the above mentioned characteristics.
There thus exists a need for medical tubing and catheters constructed of materials so that they are substantially kink-resistant and also have sufficient mechanical strength and stiffness to perform their intended functions.